Trans-septal intra-cardiac lead system

ABSTRACT

An apparatus for and method of measuring pressure through a septum in a patient&#39;s heart is disclosed. A lead inserted into the right side of a heart is routed through the septum to gain access to the left side of the heart. The lead includes an attachment structure that secures the lead to one or both of the septal walls. The attachment structure may include at least one protruding tine, membrane, inflatable balloon, involuted spiral or J-lead that engage one or more sides of the septum. The lead also includes one or more sensors for measuring cardiac pressure on the left side of the heart and, as necessary, the right side of the heart.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to copending U.S. patent applications:

1) Ser. No. 11/053,374, titled “Trans-Septal Intra-Cardiac Lead System”;

2) Ser. No. 11/053,518, tilted “Trans-Septal Intra-Cardiac Lead System”;

3) Ser. No. 11/053,494, “Trans-Septal Intra-Cardiac Lead System”;

4) Ser. No. 11/053,566, tilted “Trans-Septal Intra-Cardiac Lead System”;

5) Ser. No. 11/053,373, tilted “Trans-Septal Intra-Cardiac Lead System”;and

6) Ser. No. 11/053,468, tilted “Trans-Septal Intra-Cardiac Lead System”;

all applications filed concurrently herewith.

TECHNICAL FIELD

This application relates generally to implantable cardiac stimulationdevices and, more specifically, to a lead system implanted through aseptal wall.

BACKGROUND

When a person's heart does not function normally due to, for example, agenetic or acquired condition various treatments may be prescribed tocorrect or compensate for the condition. For example, pharmaceuticaltherapy may be prescribed for a patient or a pacemaker may be implantedin the patient to improve the operation of the patient's heart.

In conjunction with such therapy it may be desirable to measure pressurein one or more chambers of the heart. For example, absolute cardiacpressure may be used as an indicator for several potentially lethalcardiac conditions. By measuring cardiac pressure, abnormal conditionssuch as these may be detected and in some cases the patient's therapymay be modified to compensate for the abnormal conditions. As anexample, if cardiac pressure is continuously measured, the operation ofan implanted device such as a pacemaker may be adjusted, as necessary,according to conditions diagnosed as a result of the pressuremeasurements.

Conventionally, pressure sensing devices have been used to measurepressures on the right side of the heart. However, measurements of rightside pressure may not provide sufficient indications for detection ofconditions such as congestive heart failure, hypertension and mitralvalve defects. In particular, left atrial pressure has been identifiedas an excellent indicator for left ventricular failure.

Obtaining pressure measurements from the left side of the heart presentsseveral challenges. First, access to the left side of the heart must beprovided in a safe manner. In addition, the pressure sensors need to beimplanted in a manner that ensures accurate pressure measurements may bemade. Again, the use of a safe implantation technique is a primaryconsideration. Accordingly, a need exists for improved structures andtechniques for measuring cardiac pressure.

SUMMARY

The invention relates to an apparatus for and method of measuringpressure through a septal wall in a patient's heart. For convenience, anembodiment of a pressure measurement apparatus constructed according tothe invention will be referred to herein simply as an “embodiment.”

In one aspect of the invention, a lead inserted into the right side of aheart is routed through a septal wall to gain access to the left side ofthe heart. The lead includes an attachment structure that secures thelead to the septal wall. The lead also includes one or more sensors formeasuring cardiac pressure on the left side of the heart and, if needed,the right side of the heart.

In some embodiments the attachment structure is adjustable to facilitatepositioning the attachment structure against one or more septal walls.For example, an attachment structure may include two structures that arepositioned on respective sides of a septum. The position of one or bothof these structures relative to the lead may then be adjusted to placeeach structure against a respective septal wall. The lead also mayinclude structure (e.g., a spring) to bias the attachment structureagainst the walls of the septum to automatically adjust the lead to thethickness of the septal wall.

In some embodiments the attachment structure includes tines that expandoutwardly from the distal portion of the lead to engage a side of theseptal wall. Again, the lead includes one or more pressure sensors at ornear the distal end of the lead to obtain pressure measurements from theleft side of the heart and, if applicable, the right side of the heart.

In some embodiments the attachment structure includes one or moreflexible membranes that expand outwardly from the lead. Each flexiblemembrane is then positioned against a side of the septal wall. In thisway, the lead may be effectively secured to the septal wall,particularly once the intima is formed. The flexible membrane mayinclude a diaphragm that conducts pressure waves from the left side ofthe heart to a pressure sensor in the lead via a fluid-filled chamber(e.g., a lumen).

In some embodiments the attachment structure includes one or moreinflatable membranes that expand outwardly from the lead. For example,the lead may include a pair of balloon-like structures that arepositioned adjacent to the septal wall on opposite sides of the septalwall. Once the balloons are inflated, the lead may be effectivelysecured to the septal wall. The balloon also may include a diaphragmportion that conducts pressure waves from the left side of the heart toa pressure sensor in the lead via a liquid-filled chamber.

In some embodiments the attachment structure includes one or moreinvoluted spirals that expand outwardly from the distal portion of thelead to engage a side of the septal wall. Again, the lead includes oneor more pressure sensors at or near the distal end of the lead to obtainpressure measurements.

In some embodiments the lead includes a J-lead structure on its distalend for securing the lead against a septal wall. For example, the leadmay be configured to bend at a distal end that is inserted through anopening in a septal wall. In this way, the bent portion serves toprevent the lead from being pulled back through the opening. The leadincludes one or more sensors at its distal end for sensing pressureacross the septal wall.

In some embodiments additional pressure sensors may be implanted atvarious locations in the patient to provide relative pressuremeasurements. For example, a pressure sensor may be implanted in thethoracic cavity to obtain thoracic cavity pressure relative to any ofthe chambers in the heart.

In some embodiments the lead includes one or more electrodes to provideelectrical stimulation to the heart or to sense electrical activity inthe heart. For example, electrodes may be positioned on the lead toapply stimulation to or receive signals in the area of the septal wall.These electrodes may be located on or incorporated in, for example, thelead and/or an attachment structure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the invention willbe more fully understood when considered with respect to the followingdetailed description, appended claims and accompanying drawings,wherein:

FIG. 1 is a simplified diagram of one embodiment of an implantablestimulation device in electrical communication with several leadsimplanted in a patient's heart for measuring pressure and deliveringmulti-chamber stimulation and shock therapy in accordance with theinvention;

FIG. 2 is a simplified functional block diagram of one embodiment of amulti-chamber implantable stimulation device constructed in accordancewith the invention, illustrating basic elements that are configured toprovide pressure sensing, cardioversion, defibrillation or pacingstimulation or any combination thereof;

FIG. 3 is a simplified diagram of one embodiment of a cardiac leadhaving an attachment structure that is implanted through a septum inaccordance with the invention;

FIG. 4 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating an adjustable attachment structure inaccordance with the invention;

FIG. 5 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a biased attachment structure in accordancewith the invention;

FIG. 6 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating an adjustable attachment structure inaccordance with the invention;

FIG. 7 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating an attachment structure and a flexiblediaphragm in accordance with the invention;

FIG. 8 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a branch lead in accordance with theinvention;

FIG. 9 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating multiple branch leads in accordance with theinvention;

FIG. 10 is a simplified diagram of one embodiment of a cardiac leadincorporating a tine attachment structure in accordance with theinvention;

FIG. 11 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating adjustable tines in accordance with theinvention;

FIG. 12 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating biased tines in accordance with theinvention;

FIG. 13 is an end view of one embodiment of an implantable cardiac leadincorporating tines in accordance with the invention;

FIG. 14 is a simplified diagram of one embodiment of a cardiac leadhaving a membrane attachment structure that is implanted through aseptum in accordance with the invention;

FIG. 15 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating membranes in accordance with the invention;

FIG. 16 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a membrane and a distal end sensor inaccordance with the invention;

FIG. 17 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a distal end sensor in accordance with theinvention;

FIG. 18 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a distal end sensor in accordance with theinvention;

FIG. 19 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating membranes and a sheath in accordance with theinvention;

FIG. 20 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating balloons in accordance with the invention;

FIG. 21 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a balloon in accordance with the invention;

FIG. 22 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating balloons in accordance with the invention;

FIG. 23 is a simplified diagram of one embodiment of a sensorincorporating a bellow in accordance with the invention;

FIG. 24 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a sensor with a bellow in accordance with theinvention;

FIG. 25 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating involuted spirals in accordance with theinvention;

FIG. 26 is a simplified diagram of a side view of one embodiment of animplantable cardiac lead incorporating involuted spirals in accordancewith the invention;

FIG. 27 is a simplified diagram of dimensions in one embodiment of animplantable cardiac lead incorporating involuted spirals in accordancewith the invention;

FIG. 28 comprising FIGS. 28A and 28B is a simplified diagram of oneembodiment of an implantable cardiac lead incorporating involutedspirals and a stylet in accordance with the invention;

FIG. 29 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a J-lead structure in accordance with theinvention;

FIG. 30 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a J-lead structure and an attachmentstructure in accordance with the invention;

FIG. 31 is a simplified diagram of one embodiment of an implantablecardiac lead incorporating a J-lead structure and a stylet in accordancewith the invention;

FIG. 32 is a simplified flow chart of one embodiment of pressuremeasurement operations that may be performed in accordance with theinvention;

FIG. 33 is a simplified flow chart of one embodiment of pressuremeasurement operations that may be performed in accordance with theinvention;

FIG. 34 comprising FIGS. 34A-34D are simplified flow charts ofembodiments of pressure measurement operations that may be performed inaccordance with the invention; and

FIG. 35 is a simplified flow chart of one embodiment of pressuremeasurement operations that may be performed in accordance with theinvention.

In accordance with common practice the various features illustrated inthe drawings may not be drawn to scale. Accordingly, the dimensions ofthe various features may be arbitrarily expanded or reduced for clarity.In addition, some of the drawings may be simplified for clarity. Thus,the drawings may not depict all of the components of a given apparatusor method. Finally, like reference numerals denote like featuresthroughout the specification and figures.

DETAILED DESCRIPTION

The invention is described below, with reference to detailedillustrative embodiments. It will be apparent that the invention may beembodied in a wide variety of forms, some of which may be quitedifferent from those of the disclosed embodiments. Consequently, thespecific structural and functional details disclosed herein are merelyrepresentative and do not limit the scope of the invention.

Referring to FIG. 1, in one aspect the invention relates to animplantable cardiac device that includes one or more leads (e.g., lead103) that are implanted in a patient. The lead 103 consists of a leadbody and includes sensors 105 and 107 for measuring pressure in thepatient and may include one or more electrodes 109 for providingstimulation to or sensing signals in the patient's heart. Theimplantable cardiac device includes circuitry (e.g., in device 100) thatprocesses signals from the sensors 105 and 107 to determine relativecardiac pressure.

In embodiments where the lead is initially routed into the right side ofthe heart, pressure may be measured in the left side of the heart (e.g.,the left atrium, left ventricle or aorta) by routing the lead through awall in the heart (e.g., the ventricular septum 111 or the atrial septum302 shown in FIG. 3). For example, a hole may be created in the septumby piercing the septum using a separate piercing device or using a lead103 that has a piercing end.

After a distal portion of the lead 103 is maneuvered through the septum111, an attachment structure 113 that expands from the lead 103 ispositioned against a wall 115 of the septum 111. An attachment structuremay take many forms including, without limitation, one or more tines,flexible membranes, inflatable membranes, circumferential tines and/orJ-leads. In some embodiments the lead 103 includes another attachmentstructure 117 that is positioned against another wall 119 of the septum111.

In one aspect of the invention, an attachment structure is configured sothat it has a relatively low profile against the septal wall. In thisway, problems associated with protruding objects in the side of theheart may be avoided. For example, blood clots may form on an objectthat protrudes from a wall of the heart. If these blood clots breakloose in the left side of the heart the blood clots may travel to otherareas of the body such as the brain and cause a blockage in a bloodvessel (i.e., an embolism).

In contrast, the body may quickly build up a biological layer ofendothelial cells (“the intima”) over an attachment structure with arelatively low profile. As a result, the likelihood of blood clotsbreaking loose may be significantly reduced as compared to leads thatprotrude relatively deeply into the left side of the heart.

The buildup of the intima also may assist in firmly attaching theattachment structure to the septal wall. As a result, the lead may beattached to the heart in a sufficiently stable manner so as to preventinjury to the heart and provide accurate pressure measurements.

Through the use of leads that provide a secure and safe attachment tothe septal wall and, in some case, other leads and sensors (e.g., lead125 and sensor 127) implanted in the patient, the implantable cardiacdevice may be used to provide a variety of pressure measurements in realtime. These cardiac pressure measurements may provide valuableinformation for diagnosing a variety of cardiac problems. Table 1 listsseveral examples of cardiac problems that may be associated with low orhigh pressure measurements in the left atrium (“LA”), right atrium(“RA”), left ventricle (“LV”) or right ventricle (“RV”).

TABLE 1 LA RA LV RV High Mitral Atrial Mitral regurgitation; Tricuspidpressure stenosis; septal Aortic regurgitation; regurgitation; detectedLV failure defects Congestive heart Pulmonary failure; stenosis HOCM;Septal infarction; Hypertension Low LV failure; Tricuspid pressureVentricular septal stenosis detected defect; Congestive heart failure

When diagnoses such as these are used in conjunction with a heartstimulation device, appropriate therapy such as cardiacresynchronization therapy may be immediately delivered to the patient.Additional details of an exemplary stimulation device will be discussedin conjunction with FIGS. 1 and 2.

Exemplary Stimulation Device

The following description sets forth but one exemplary stimulationdevice that is capable of being used in connection with the variousembodiments that are described below. It is to be appreciated andunderstood that other stimulation devices, including those that are notnecessarily implantable, can be used and that the description below isgiven, in its specific context, to assist the reader in understanding,with more clarity, the inventive embodiments described herein.

FIG. 1 shows an exemplary stimulation device 100 in electricalcommunication with a patient's heart 102 by way of three leads 104, 106,and 108, suitable for delivering multi-chamber stimulation and shocktherapy. To sense atrial cardiac signals and to provide right atrialchamber stimulation therapy, stimulation device 100 is coupled to animplantable right atrial lead 104 having at least an atrial tipelectrode 120, which typically is implanted in the patient's rightatrial appendage or septum. FIG. 1 shows the right atrial lead 104 ashaving an optional atrial ring electrode 121.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, stimulation device 100 is coupled to a coronarysinus lead 106 designed for placement in the coronary sinus region viathe coronary sinus for positioning a distal electrode adjacent to theleft ventricle and/or additional electrode(s) adjacent to the leftatrium. As used herein, the phrase “coronary sinus region” refers to thevasculature of the left ventricle, including any portion of the coronarysinus, great cardiac vein, left marginal vein, left posteriorventricular vein, middle cardiac vein, and/or small cardiac vein or anyother cardiac vein accessible by the coronary sinus.

Accordingly, an exemplary coronary sinus lead 106 is designed to receiveatrial and ventricular cardiac signals and to deliver left ventricularpacing therapy using at least a left ventricular tip electrode 122, leftventricular ring electrode 123, left atrial pacing therapy using atleast a left atrial ring electrode 124, and shocking therapy using atleast a left atrial coil electrode 126 (or other electrode capable ofdelivering a shock). For a complete description of a coronary sinuslead, the reader is directed to U.S. Pat. No. 5,466,254, “Coronary SinusLead with Atrial Sensing Capability” (Helland), which is incorporatedherein by reference.

Stimulation device 100 is also shown in electrical communication withthe patient's heart 102 by way of an implantable right ventricular lead108 having, in this implementation, a right ventricular tip electrode128, a right ventricular ring electrode 130, a right ventricular (RV)coil electrode 132 (or other electrode capable of delivering a shock),and superior vena cava (SVC) coil electrode 134 (or other electrodecapable of delivering a shock). Typically, the right ventricular lead108 is transvenously inserted into the heart 102 to place the rightventricular tip electrode 128 in the right ventricular apex so that theRV coil electrode 132 will be positioned in the right ventricle and theSVC coil electrode 134 will be positioned in the superior vena cava.Accordingly, the right ventricular lead 108 is capable of sensing orreceiving cardiac signals, and delivering stimulation in the form ofpacing and shock therapy to the right ventricle.

FIG. 2 shows an exemplary, simplified block diagram depicting variouscomponents of stimulation device 100. The stimulation device 100 can becapable of treating both fast and slow arrhythmias with stimulationtherapy, including cardioversion, defibrillation, and pacingstimulation. While a particular multi-chamber device is shown, it is tobe appreciated and understood that this is done for illustrationpurposes only. Thus, the techniques and methods described below can beimplemented in connection with any suitably configured or configurablestimulation device. Accordingly, one of skill in the art could readilyduplicate, eliminate, or disable the appropriate circuitry in anydesired combination to provide a device capable of treating theappropriate chamber(s) with cardioversion, defibrillation, and pacingstimulation.

Housing 200 for stimulation device 100 is often referred to as the“can”, “case” or “case electrode”, and may be programmably selected toact as the return electrode for all “unipolar” modes. Housing 200 mayfurther be used as a return electrode alone or in combination with oneor more of the coil electrodes 126, 132 and 134 for shocking purposes.Housing 200 further includes a connector (not shown) having a pluralityof terminals 202, 204, 206, 208, 212, 214, 216, and 218 (shownschematically and, for convenience, the names of the electrodes to whichthey are connected are shown next to the terminals).

To achieve right atrial sensing and pacing, the connector includes atleast a right atrial tip terminal (AR TIP) 202 adapted for connection tothe atrial tip electrode 120. A right atrial ring terminal (AR RING) 203may also be included adapted for connection to the atrial ring electrode121. To achieve left chamber sensing, pacing, and shocking, theconnector includes at least a left ventricular tip terminal (VL TIP)204, left ventricular ring terminal (VL RING) 205, a left atrial ringterminal (AL RING) 206, and a left atrial shocking terminal (AL COIL)208, which are adapted for connection to the left ventricular tipelectrode 122, the left atrial ring electrode 124, and the left atrialcoil electrode 126, respectively.

To support right chamber sensing, pacing, and shocking, the connectorfurther includes a right ventricular tip terminal (VR TIP) 212, a rightventricular ring terminal (VR RING) 214, a right ventricular shockingterminal (RV COIL) 216, and a superior vena cava shocking terminal (SVCCOIL) 218, which are adapted for connection to the right ventricular tipelectrode 128, right ventricular ring electrode 130, the RV coilelectrode 132, and the SVC coil electrode 134, respectively.

At the core of the stimulation device 100 is a programmablemicrocontroller 220 that controls the various modes of stimulationtherapy. As is well known in the art, microcontroller 220 typicallyincludes a microprocessor, or equivalent control circuitry, designedspecifically for controlling the delivery of stimulation therapy, andmay further include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and I/O circuitry. Typically, microcontroller 220includes the ability to process or monitor input signals (data orinformation) as controlled by a program code stored in a designatedblock of memory. The type of microcontroller is not critical to thedescribed implementations. Rather, any suitable microcontroller 220 maybe used that carries out the functions described herein. The use ofmicroprocessor-based control circuits for performing timing and dataanalysis functions are well known in the art.

Representative types of control circuitry that may be used in connectionwith the described embodiments can include the microprocessor-basedcontrol system of U.S. Pat. No. 4,940,052 (Mann et al.), thestate-machine of U.S. Pat. Nos. 4,712,555 (Thornander et al.) and4,944,298 (Sholder), all of which are incorporated by reference herein.For a more detailed description of the various timing intervals usedwithin the stimulation device and their inter-relationship, see U.S.Pat. No. 4,788,980 (Mann et al.), also incorporated herein by reference.

FIG. 2 also shows an atrial pulse generator 222 and a ventricular pulsegenerator 224 that generate pacing stimulation pulses for delivery bythe right atrial lead 104, the coronary sinus lead 106, and/or the rightventricular lead 108 via an electrode configuration switch 226. It isunderstood that in order to provide stimulation therapy in each of thefour chambers of the heart, the atrial and ventricular pulse generators,222 and 224, may include dedicated, independent pulse generators,multiplexed pulse generators, or shared pulse generators. The pulsegenerators 222 and 224 are controlled by the microcontroller 220 viaappropriate control signals 228 and 230, respectively, to trigger orinhibit the stimulation pulses.

Microcontroller 220 further includes timing control circuitry 232 tocontrol the timing of the stimulation pulses (e.g., pacing rate,atrio-ventricular (AV) delay, atrial interconduction (A-A) delay, orventricular interconduction (V-V) delay, etc.) as well as to keep trackof the timing of refractory periods, blanking intervals, noise detectionwindows, evoked response windows, alert intervals, marker channeltiming, etc., which is well known in the art.

Microcontroller 220 further includes an arrhythmia detector 234, amorphology detector 236, and optionally an orthostatic compensator and aminute ventilation (MV) response module, the latter two are not shown inFIG. 2. These components can be utilized by the stimulation device 100for determining desirable times to administer various therapies,including those to reduce the effects of orthostatic hypotension. Theaforementioned components may be implemented in hardware as part of themicrocontroller 220, or as software/firmware instructions programmedinto the device and executed on the microcontroller 220 during certainmodes of operation.

The electronic configuration switch 226 includes a plurality of switchesfor connecting the desired electrodes to the appropriate I/O circuits,thereby providing complete electrode programmability. Accordingly,switch 226, in response to a control signal 242 from the microcontroller220, determines the polarity of the stimulation pulses (e.g., unipolar,bipolar, combipolar, etc.) by selectively closing the appropriatecombination of switches (not shown) as is known in the art.

Atrial sensing circuits 244 and ventricular sensing circuits 246 mayalso be selectively coupled to the right atrial lead 104, coronary sinuslead 106, and the right ventricular lead 108, through the switch 226 fordetecting the presence of cardiac activity in each of the four chambersof the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR.SENSE) sensing circuits, 244 and 246, may include dedicated senseamplifiers, multiplexed amplifiers, or shared amplifiers. Switch 226determines the “sensing polarity” of the cardiac signal by selectivelyclosing the appropriate switches, as is also known in the art. In thisway, the clinician may program the sensing polarity independent of thestimulation polarity. The sensing circuits (e.g., 244 and 246) areoptionally capable of obtaining information indicative of tissuecapture.

Each sensing circuit 244 and 246 preferably employs one or more lowpower, precision amplifiers with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit, as knownin the art, to selectively sense the cardiac signal of interest. Theautomatic gain control enables the device 100 to deal effectively withthe difficult problem of sensing the low amplitude signalcharacteristics of atrial or ventricular fibrillation.

The outputs of the atrial and ventricular sensing circuits 244 and 246are connected to the microcontroller 220, which, in turn, is able totrigger or inhibit the atrial and ventricular pulse generators 222 and224, respectively, in a demand fashion in response to the absence orpresence of cardiac activity in the appropriate chambers of the heart.Furthermore, as described herein, the microcontroller 220 is alsocapable of analyzing information output from the sensing circuits 244and 246 and/or the data acquisition system 252 to determine or detectwhether and to what degree tissue capture has occurred and to program apulse, or pulses, in response to such determinations. The sensingcircuits 244 and 246, in turn, receive control signals over signal lines248 and 250 from the microcontroller 220 for purposes of controlling thegain, threshold, polarization charge removal circuitry (not shown), andthe timing of any blocking circuitry (not shown) coupled to the inputsof the sensing circuits, 244 and 246, as is known in the art.

For arrhythmia detection, the device 100 utilizes the atrial andventricular sensing circuits, 244 and 246, to sense cardiac signals todetermine whether a rhythm is physiologic or pathologic. In reference toarrhythmias, as used herein, “sensing” is reserved for the noting of anelectrical signal or obtaining data (information), and “detection” isthe processing (analysis) of these sensed signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., P-waves, R-waves, and depolarization signals associated withfibrillation which are sometimes referred to as “F-waves” or“Fib-waves”) are then classified by the arrhythmia detector 234 of themicrocontroller 220 by comparing them to a predefined rate zone limit(i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillationrate zones) and various other characteristics (e.g., sudden onset,stability, physiologic sensors, and morphology, etc.) in order todetermine the type of remedial therapy that is needed (e.g., bradycardiapacing, anti-tachycardia pacing, cardioversion shocks or defibrillationshocks, collectively referred to as “tiered therapy”).

Cardiac signals are also applied to inputs of an analog-to-digital (A/D)data acquisition system 252. The data acquisition system 252 isconfigured (e.g., via signal line 251) to acquire intracardiacelectrogram signals, convert the raw analog data into a digital signal,and store the digital signals for later processing and/or telemetrictransmission to an external device 254. The data acquisition system 252is coupled to the right atrial lead 104, the coronary sinus lead 106,and the right ventricular lead 108 through the switch 226 to samplecardiac signals across any pair of desired electrodes.

The microcontroller 220 is further coupled to a memory 260 by a suitabledata/address bus 262, wherein the programmable operating parameters usedby the microcontroller 220 are stored and modified, as required, inorder to customize the operation of the stimulation device 100 to suitthe needs of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, waveshape and vector of each shocking pulse to bedelivered to the patient's heart 102 within each respective tier oftherapy. One feature of the described embodiments is the ability tosense and store a relatively large amount of data (e.g., from the dataacquisition system 252), which data may then be used for subsequentanalysis to guide the programming of the device.

Advantageously, the operating parameters of the implantable device 100may be non-invasively programmed into the memory 260 through a telemetrycircuit 264 in telemetric communication via communication link 266 withthe external device 254, such as a programmer, transtelephonictransceiver, or a diagnostic system analyzer. The microcontroller 220activates the telemetry circuit 264 with a control signal 268. Thetelemetry circuit 264 advantageously allows intracardiac electrogramsand status information relating to the operation of the device 100 (ascontained in the microcontroller 220 or memory 260) to be sent to theexternal device 254 through an established communication link 266.

The stimulation device 100 can further include a physiologic sensor 270,commonly referred to as a “rate-responsive” sensor because it istypically used to adjust pacing stimulation rate according to theexercise state of the patient. However, the physiological sensor 270 mayfurther be used to detect changes in cardiac output, changes in thephysiological condition of the heart, or diurnal changes in activity(e.g., detecting sleep and wake states). Accordingly, themicrocontroller 220 responds by adjusting the various pacing parameters(such as rate, AV Delay, V-V Delay, etc.) at which the atrial andventricular pulse generators, 222 and 224, generate stimulation pulses.While shown as being included within the stimulation device 100, it isto be understood that the physiologic sensor 270 may also be external tothe stimulation device 100, yet still be implanted within or carried bythe patient. Examples of physiologic sensors that may be implemented indevice 100 include known sensors that, for example, sense respirationrate, pH of blood, ventricular gradient, oxygen saturation, bloodpressure and so forth. Another sensor that may be used is one thatdetects activity variance, wherein an activity sensor is monitoreddiurnally to detect the low variance in the measurement corresponding tothe sleep state. For a more detailed description of an activity variancesensor, the reader is directed to U.S. Pat. No. 5,476,483 (Bornzin etal.), issued Dec. 19, 1995, which patent is hereby incorporated byreference.

More specifically, the physiological sensors 270 optionally includesensors to help detect movement and minute ventilation in the patient.The physiological sensors 270 may include a position sensor and/or aminute ventilation (MV) sensor to sense minute ventilation, which isdefined as the total volume of air that moves in and out of a patient'slungs in a minute. Signals generated by the position sensor and MVsensor are passed to the microcontroller 220 for analysis in determiningwhether to adjust the pacing rate, etc. The microcontroller 220 monitorsthe signals for indications of the patient's position and activitystatus, such as whether the patient is climbing upstairs or descendingdownstairs or whether the patient is sitting up after lying down.

The stimulation device additionally includes a battery 276 that providesoperating power to all of the circuits shown in FIG. 2. For thestimulation device 100, which employs shocking therapy, the battery 276is capable of operating at low current drains for long periods of time(e.g., preferably less than 10 μA), and is capable of providinghigh-current pulses (for capacitor charging) when the patient requires ashock pulse (e.g., preferably, in excess of 2 A, at voltages above 200V, for periods of 10 seconds or more). The battery 276 also desirablyhas a predictable discharge characteristic so that elective replacementtime can be detected.

The stimulation device 100 can further include magnet detectioncircuitry (not shown), coupled to the microcontroller 220, to detectwhen a magnet is placed over the stimulation device 100. A magnet may beused by a clinician to perform various test functions of the stimulationdevice 100 and/or to signal the microcontroller 220 that the externalprogrammer 254 is in place to receive or transmit data to themicrocontroller 220 through the telemetry circuits 264.

The stimulation device 100 further includes an impedance measuringcircuit 278 that is enabled by the microcontroller 220 via a controlsignal 280. The known uses for an impedance measuring circuit 278include, but are not limited to, lead impedance surveillance during theacute and chronic phases for proper performance, lead positioning ordislodgement; detecting operable electrodes and automatically switchingto an operable pair if dislodgement occurs; measuring respiration orminute ventilation; measuring thoracic impedance for determining shockthresholds; detecting when the device has been implanted; measuringstroke volume; and detecting the opening of heart valves, etc. Theimpedance measuring circuit 278 is advantageously coupled to the switch226 so that any desired electrode may be used.

In the case where the stimulation device 100 is intended to operate asan implantable cardioverter/defibrillator (ICD) device, it detects theoccurrence of an arrhythmia, and automatically applies an appropriatetherapy to the heart aimed at terminating the detected arrhythmia. Tothis end, the microcontroller 220 further controls a shocking circuit282 by way of a control signal 284. The shocking circuit 282 generatesshocking pulses of low (e.g., up to 0.5 J to 2.0 J), moderate (e.g., 2.5J to 10 J), or high energy (e.g., 11 J to 40 J), as controlled by themicrocontroller 220. Such shocking pulses are applied to the patient'sheart 102 through at least two shocking electrodes, and as shown in thisembodiment, selected from the left atrial coil electrode 126, the RVcoil electrode 132, and/or the SVC coil electrode 134. As noted above,the housing 200 may act as an active electrode in combination with theRV electrode 132, and/or as part of a split electrical vector using theSVC coil electrode 134 or the left atrial coil electrode 126 (i.e.,using the RV electrode as a common electrode).

Cardioversion level shocks are generally considered to be of low tomoderate energy level (so as to minimize pain felt by the patient),and/or synchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5 J to40 J), delivered asynchronously (since R-waves may be too disorganized),and pertaining exclusively to the treatment of fibrillation.Accordingly, the microcontroller 220 is capable of controlling thesynchronous or asynchronous delivery of the shocking pulses.

Pressure Sensors and Related Components

In some embodiments device 100 also may include circuitry for processingsignals from one or more pressure sensors. Depending upon theapplication, the pressure sensors may be implanted in the heart, inother locations in the patient such as the thoracic cavity, anywherealong a lead or within the housing 200.

A typical pressure sensor generates electrical signals indicative ofchanges in a sensed pressure. Thus, one or more wires may be used toconnect a sensor to the device 100. FIG. 2 illustrates an embodimentwhere two pressure signals P1 and P2 are coupled to the device 100 viaterminals 211 and 213, respectively. An analog-to-digital (A/D) dataacquisition system 253 may be configured (e.g., via signal line 255) toacquire and amplify the signals P1 and P2, convert the raw analog datainto a digital signal, filter the signals and store the digital signalsfor later processing by, for example, a pressure measurement processingcomponent 286 and/or telemetric transmission to an external device 254.

Referring now to FIGS. 3-7, various embodiments of leads thatincorporate an attachment structure on their distal portion for fixingthe lead to a wall in the heart will be discussed. FIG. 3 depicts oneexample of how a lead may be implanted through a septum (the atrialseptum in this example) in the heart. FIGS. 4-7 depict severalembodiments of leads and illustrate various components that may beincorporated into a lead.

In general, the attachment structure is positioned against the wall in amanner that may prevent the lead from moving relative to the wall. Inthis way, the attachment structure serves to effectively attach the leadto the wall.

The leads include a sensor and, in some embodiments, componentsassociated with a sensor (hereafter collectively referred to as a sensorfor convenience) on their distal portions. This sensor may be entirelyor partially positioned in the left side of the heart when the lead isimplanted. In this way the lead may be used to monitor pressure in theleft side of the heart.

In FIG. 3 a lead 300 includes a lead body 304 that may house one or moreelectrical conductors, fluid-carrying lumens and/or other components(not shown). The distal end of the lead 300 may be initially introducedinto the heart via the right atrium (“RA”) using known techniques. Forexample, the lead 300 may contain a stylet 312 that enables the lead 300to be manipulated in a desired direction in the heart.

To pass the lead 300 through to the left atrium (“LA”), the atrialseptal wall may be pierced using, for example, a piercing tool (notshown) or using a lead 300 that includes on its distal end a relativelysharp and hard tip (not shown). In either case the piercing apparatus ismanipulated to create an access tunnel 306 in the septum. The accesstunnel 306 may be made in the region of the fossa ovalis since this maybe the thinnest portion of the atrial septum 302.

The distal portion of the lead 300 is then maneuvered through the atrialseptum 302 (e.g., using the stylet) so that all or a portion of apressure sensor 308 at the distal end of the lead 300 protrudes into theleft atrium. In this way, the sensor 308 may be used to accuratelymeasure pressure in the left atrium.

The lead 300 also may include a pressure sensor 318 positionedproximally on the lead from the sensor 308. The sensor 318 may thus beused to accurately measure pressure in the right atrium. The lead 300includes an attachment structure that serves to attach the lead 300 tothe septum 302. The attachment structure may take many forms including,without limitation, one or more tines, flexible membranes, inflatablemembranes, circumferential tines and/or J-leads. FIG. 3 represents theattachment structure in a generalized manner. More specific examples ofattachment structures are discussed below in conjunction with FIGS.10-31.

In the embodiment of FIG. 3, the attachment structure includes a firstattachment structure 310 and a second attachment structure 314 implantedon opposite sides of the septum. In other applications a singleattachment structure may be implanted on one of the sides of the septum.It should be understood that the components, configurations andtechniques described herein may be applicable to an attachment structurethat is implanted on one or more sides of a septum.

The first attachment structure 310 is attached to the distal portion ofthe lead 300. After the first attachment structure 310 is pushed throughthe access tunnel 306, it expands outwardly from the lead 300 such thatit tends to prevent the distal end of the lead 300 from being pulledback through the access tunnel 306. The first attachment structure 310is then positioned against a septal wall in the left atrium.

The second attachment structure 314 extends outwardly from the lead 300to help prevent the lead 300 from sliding further down into the leftatrium. As FIG. 3 illustrates, the second attachment structure 314 ispositioned against a septal wall in the right atrium.

In some embodiments the attachment structures 310 and 314 are positioneda pre-defined distance apart on the lead 300. For example, the lead maybe constructed so that the spacing between the attachment structures 310and 314 is approximately equal to the thickness of the septum in thearea of the access tunnel 306.

In some embodiments one or more of the attachment structures 310 and 314are attached to the lead 300 in a manner that enables the position ofthe attachment structure to be adjusted. For example, one or both of theattachment structures 310 and 314 may be slidably mounted to the lead300 so that they may be moved toward one another to firmly place eachattachment structure against the septum 302. Such movement of theattachment structures 310 and 314 may be accomplished, for example, by amanual operation (e.g., via a tensile member such as a stylet or asheath) or automatically through the use of a biasing member (e.g., aspring).

The lead 300 also may include an electrode 320 that may be used to applystimulation signals to the septum. For example, a circumferentialelectrode such as a ring electrode may be located between the first andsecond attachment structures 310 and 314.

FIG. 3 also illustrates that various control apparatus 322 may beattached to the proximal end of the lead 300. For example, mechanismsmay be provided for moving stylets or guide wires 312, movable sheathsor other components (not shown) in the lead 300 or for controlling theflow of fluid through lumens in the lead 300. In some applications, thecontrol apparatus 322 may be removed from the lead 300 when the device100 (not shown) attached to proximal end of the lead is implanted in thepatient.

The embodiment of FIG. 3 may provide highly accurate pressuremeasurements because the right side and left side pressures may bemeasured using a single intra cardiac lead. As a result, the number ofvariables affecting the measurements may be significantly reduced usingthis approach as compared to approaches that measure different pressuresusing more than one lead. Moreover, as discussed below, by measuring thepressure gradient across two locations, factors such as drift may beless of a problem as compared to conventional systems that measure thepressure gradient by referencing pressure measurements at each locationto a vacuum.

By providing accurate left and right atrium pressure information theembodiment of FIG. 3 may be used to diagnose septal defects (pressuregradient in septal defects is approximately zero) or other cardiacconditions in which therapeutic intervention may be required. Moreover,these pressure measurements may be referenced to pressure in otherareas. For example, thoracic pressure may be used as a transmuralreference.

Finally, as discussed above in conjunction with FIG. 1 a trans-septallead as taught herein may be used to measure pressures in the left andright ventricles to diagnose various cardiac conditions. Thus, a leadsimilar to the one described in FIG. 3 and the figures that follow maybe implanted across the ventricular septum.

Referring now to FIGS. 4-7, additional details of various embodiments ofleads will be described. These examples also describe the attachmentstructure in a generic form.

In FIG. 4 the distal end of a lead 400 is shown implanted through anaccess tunnel 402 in a septum 404 (e.g., the atrial or ventricularseptum). The lead 400 includes a pressure sensor 406 mounted on thedistal end of the lead 400 for measuring pressure in the left side ofthe heart. The lead 400 also includes a pressure sensor 408 that is usedto measure pressure in the right side of the heart.

The lead 400 includes a first attachment structure 410 on its distal endand a second attachment structure 412 mounted proximally on the lead tothe first attachment structure 410. The attachment structure 412 isslidably mounted to the lead 400 so that the attachment structure 412may be moved toward the attachment structure 410 to firmly attach thelead 400 to the septum 404.

Movement of the attachment structure 412 is accomplished by moving atensile member 414 in a longitudinal direction through the lead 400. Insome embodiments, the tensile member 414 may be carried within a lumen416 that facilitates sliding of the tensile member (“stylet) 414. Theproximal end of the tensile member 414 may then be attached to a handleor other structure (not shown) that enables the physician to slide thetensile member 414.

The tensile member 414 attaches to the attachment structure 412 via afastener mechanism 418. This attachment may be accomplished, forexample, using a weld, adhesive, threads or other techniques. In someembodiments the fastener mechanism 418 passes though a slot 420 in thelead 400 so that translational movement of the tensile member 414 causesthe attachment structure 412 to slide along the lead 400. In theembodiment of FIG. 4, the attachment structure 412 includes a surface422 that slides over an outer surface 424 of the lead 400.

The dashed lines 426 represent the position of the attachment structure412 and the tensile member 414 when the tensile member 414 is slidtoward the distal end of the lead 400. In this position, the first andsecond attachment structures 410 and 412 may be firmly pressed againstthe septal walls 426 and 428, respectively. In addition, the buildup ofthe intima also may assist in firmly attaching the attachment structures410 and 412 to the septal walls.

For embodiments that include an opening (e.g., slot 420) to facilitatetranslational movement of an attachment structure, the lead 400 also mayinclude a seal 430 that prevents fluid from flowing up the lead 400.Alternatively, the opening (e.g., slot 420) may include a seal thatseals around the fastener mechanism 418 to prevent fluid from flowinginto the lead 400.

FIG. 4 also depicts an embodiment where one or more of the attachmentsstructures 410 and 412 may include one or more electrodes 432. Theelectrodes 432 may be used, for example, to pace the septum or to sensesignals in the area of the septum.

To reduce the complexity of FIG. 4, the electrical connections andassociated conductors for the sensors 406 and 408 and the electrodes 432are not illustrated. Typically, these electrical conductors will beenclosed in a lumen in the lead 400 that carries the conductors to thedevice 100 (not shown).

FIG. 5 illustrates the distal end of an embodiment of a lead 500 wherean attachment structure 502 is biased toward a septal wall 504 by abiasing member 506 (e.g., a spring). In this case the lead 500 includesa fastener mechanism 508 for connecting one end of the biasing member506 to the lead 500. In addition, a fastener mechanism 510 facilitatesconnection of the other end of the biasing member 506 to the attachmentstructure 502.

As discussed above in conjunction with FIG. 4, the lead 500 may includean opening 512 that accommodates a protrusion 516 of the fastenermechanism 510 such that translational movement of one end of the biasingmember 506 causes translational movement of the attachment structure 502along the lead 500.

In some embodiments, the lead 500 may include a tensile member 518 thatmay be used to pull the attachment structure 502 away from the distalend of the lead 500. This may be used, for example, to pull theattachment structure 502 away from the septal wall 504 when the distalend of the lead 500 is being inserted into the access tunnel to place anattachment structure 522 in the left side of the heart. After theattachment structure 522 is in place, the tensile member 518 may bereleased to enable the biasing member 506 to bias the attachmentstructure 502 against the septal wall 504.

FIG. 5 also illustrates an embodiment where an electrode ring 524 isprovided on the circumference of the lead 500. The electrode ring 524 islocated between the attachment structures 502 and 522 so that it maycome in contact with the septum in the access tunnel 520. The electrodering 524 may then be used, for example, to pace the septum or sensesignals in the septal area.

FIG. 6 illustrates the distal end of an embodiment of a lead 600 wherean attachment structure 602 may be slid along the lead 600 using asheath 604. The sheath 604 may be provided on the outside of the lead600 and is configured to slide relative to the lead as indicated by thearrows 606. As illustrated in FIG. 6, an inner surface 608 of the sheath604 slides on an outer surface 610 of the lead. Similarly, an innersurface 612 of the attachment structure 602 slides on the outer surface610 of the lead 600. By sliding the sheath 604 toward the distal end ofthe lead 600, the attachment structure 602 may be positioned (asrepresented by dashed lines 614) against a septal wall 616.

In some embodiments, the lead 600 includes a fastener mechanism 628 forconnecting one end of the sheath 604 to the attachment structure 602. Inthis way the sheath 604 may move the attachment structure 602 in eitherdirection along the length of the lead 600 as represented by the arrows606. Alternatively, the sheath 604 may not be attached to the attachmentstructure 602. In this case, the sheath may be used to push theattachment structure 602 toward the septal wall 616. As is known in theart, the proximal side of the sheath 604 may be attached to a handle orsome other structure that facilitates sliding the sheath 604.

FIG. 6 also illustrates an embodiment where a pressure sensor 618 may beplaced anywhere along the length of the lead 600. In this case, aflexible diaphragm 620 is provided on the distal end of the lead 600that protrudes into the left side of the heart. In addition, a chamber622 filled with a fluid medium is provided between the flexiblediaphragm 620 and the pressure sensor 618. Thus, pressure variations inthe left side of the heart cause the flexible diaphragm 620 to movewhich, in turn, creates pressure waves in the fluid medium.

The pressure sensor 618 senses the pressure waves in the fluid mediumand generates corresponding electrical signals that are sent to thedevice 100 (not shown) via one or more electrical conductors 624. In atypical embodiment, the pressure sensor 618 includes a flexiblediaphragm 626 and a chip (e.g., a piezoelectric element, not shown) thatgenerates electrical signals in response to pressure waves that aregenerated inside the sensor when the flexible diaphragm 626 moves. Thatis, inside the pressure sensor, pressure waves signal are conducted fromthe flexible diaphragm 626 to the chip.

A variety of fluids or gels may be used in the chamber 622. For example,the fluid may consist of a gas or an incompressible, biocompatibleliquid such as water, saline or silicone oil. The gel may be made of asilicone gel, polyacrylamide or any other biocompatible gel. In someapplications the fluid and/or gel needs to be compatible with gassterilization procedures that may be used to sterilize the lead.

The flexible diaphragm 620 may be formed in various shapes andconstructed of various materials. For example, the flexible diaphragmmay be constructed of a biocompatible material such as silicone rubber,polyurethane or metal. The metal may be, for example, titanium, platinumor Nitinol, and may preferably be thin walled. Shaping of the metal intoa bellow allows for a high degree of flexibility for pressure transfer.

FIG. 7 illustrates an embodiment of a lead 700 where a pressure sensor702 located in the device 100 may measure pressure across a septum 704.The lead 700 includes a flexible diaphragm 706 that may be implantedthrough the septum into the left side of the heart. As illustrated inFIG. 7, the flexible diaphragm may be attached to attachment structure710 as discussed herein that serves to fix the lead 700 to the septum704.

A fluid-filled lumen 708 carries pressure waves from the flexiblediaphragm 706 to the sensor 702. The lumen 708 interfaces with thesensor 702 such that pressure waves carried by the fluid in the lumen708 are provided to a flexible diaphragm 722 in the sensor 702.

FIG. 7 also illustrates the electrical connections between a pair ofelectrodes 712 and 714 and the device 100. A first electrical conductor716 is connected to the electrode 712 located to pace/sense the septumarea. A second electrical conductor 718 is connected to the electrode714 that may serve, for example, as the second electrode of a bipolarelectrode that includes electrode 712. Both of the conductors 716 and718 are routed through a lumen 720 through the lead 700 to the device100.

Referring now to FIGS. 8 and 9, leads incorporating one or more branchleads will be described. In general, any of the leads and leadcomponents described herein may be used in conjunction with such a lead.

FIG. 8 illustrates an embodiment of a lead 800 that includes a branchlead 804 with a sensor 806. As discussed above, the lead 800 may includecomponents for measuring trans-septal pressure. For example, the lead800 may include a pair of attachment structures (e.g., tines, flexiblemembranes, etc.) 808 and 810, a pair of sensors 812 and 814, anelectrode 816 and a piercing/tunneling tip 818 at its distal end.

As FIG. 8 illustrates, the sensor 806 may be located at or near thedistal end of the branch lead 804. The branch lead 804 also may includea tip 820 (e.g., a boring screw or a set of tines) that facilitatesattaching the branch lead 804 to heart tissue. For example, the branchlead 804 may be adapted to be located in the right ventricle to measureright ventricle pressure. In this case the branch lead 804 may bedirected into the right ventricle (e.g., via a guide wire), then the tip820 is manipulated to attach to the wall of the right ventricle tosecurely fix the branch lead 804 in the right ventricle.

It should be appreciated that such a branch lead may take many forms.For example, the branch lead may include the components described abovein conjunction with lead 108 or any other components described herein.For example, a branch lead may include one or more electrodes 828 forpacing or sensing. Also, a branch lead may incorporate one or more ofthe attachment structures disclosed herein.

FIG. 8 also illustrates that the sensors 806, 812 and 814 maycommunicate with the device 100 via multiplexed signals. For example, asignal circuit 822 in the device 100 may communicate with signalcircuits 824A-C associated with each sensor. These signal circuits mayinclude circuitry that multiplexes and demultiplexes the pressuresignals and generates digital or digital-like signals, e.g., pulse wavemodulated signals that are sent to the device 100. In this way, thepressure signals may be sent from each of the sensors 806, 812 and 814to the device 100 via a single connection 826. In addition, the device100 may send control signals to the sensor circuits 824A-C to, forexample, poll the sensors for pressure measurements.

FIG. 9 illustrates an embodiment of a lead 900 that includes two branchleads 904 and 906 having sensors 908 and 910, respectively. The distalportion of the main lead 900 and the branch lead 904 may includecomponents similar to those in the embodiment of FIG. 8.

The sensor 910 may be located at or near the distal end of the branchlead 906. The branch lead 906 also may include a tip 914 (e.g., a boringscrew or a set of tines) that facilitates attaching the branch lead 906to heart tissue. For example, the branch lead 906 may be configured tobe located in the right atrium to measure transmural pressure. In thiscase, branch lead 906 may be directed into the right atrium with thelead 900, then the tip 914 is manipulated to bore into a wall of theright atrium to securely fix the branch lead 906 in the right atrium.

Again it should be appreciated that such a branch lead may take manyforms. For example, the branch lead may include the components describedabove in conjunction with lead 104.

FIG. 9 also illustrates that the lead 900 may include a temporary lumen(e.g., sheath) 912 that holds the branches together during the initialimplantation process. Use of a lumen may provide improvedmaneuverability during lead implant. For example, the lumen 912 may beplaced over the branches until the septum lead (e.g., the distal portionof the main lead 900) is implanted. Then the lumen may be drawn back,enabling the branch 904 to be installed in the right ventricle asdiscussed above in conjunction with FIG. 8. Finally, the lumen 912 maybe removed to enable the branch 906 to be implanted in, for example, theright atrium. In some embodiments the construction of the lumen 912 maybe similar to that of a catheter used for implanting leads.

It should be appreciated that a variety of lead structures andconfigurations may be used in accordance with the teachings herein. Forexample, a typical lead may include separate lumens for housing guidewires and the electrical leads for the sensors and the electrodes. Inaddition, a lead body (e.g., lead body 304) may be constructed out of avariety of biocompatible materials such as MP35N, platinum, silicone andpolyurethane.

Similarly, a variety of different attachment structures may be used inaccordance with the teachings herein. For example, one or moreattachment structures may be incorporated into a lead. Moreover, a leadmay include one or more of the various types attachment structuresdescribed herein.

In addition, the attachment structures may be configured to beextendable and/or retractable. This latter configuration may provide,for example, improved maneuverability; particularly when tunnelingacross the septum.

An attachment structure may be constructed of a variety of materialsincluding, for example, biocompatible materials such as silicone andpolyurethane. The attachment structure may be metallic or non-metallic.In some embodiments the attachment structure may be constructed of abiodegradable material that degrades over time. This type of materialmay be used, for example, in a case where it may be necessary to removethe lead sometime in the future.

The leads may incorporate various types of electrodes and theseelectrodes may be implemented in various locations on the leads. Ingeneral, any of the electrodes described herein may be used inconjunction with the leads described herein.

In addition, a variety of different sensor structures may be used inaccordance with the teachings herein. For example, a typical sensorincludes a pressure transducer such as a piezoelectric chip that ismounted in a package that has a flexible diaphragm on at least a portionof its outer surface. The package is then incorporated into the intracardiac lead so that the flexible diaphragm is exposed to a heartchamber or to a fluid-filled lumen or chamber that transmits pressurewaves from the heart chamber. Thus, when the pressure changes in thechamber the flexible diaphragm will transmit a pressure wave to thepiezoelectric device. The piezoelectric device then generates anelectrical signal that may, for example, correspond to the magnitude ofthe change in pressure. It should be understood, however, that manyother forms of sensors may be used in a lead constructed according tothe invention. Moreover, in general, any of the sensors described hereinmay be used in conjunction with the leads described herein.

Referring now to FIGS. 10-13, various embodiments of leads thatincorporate one or more tine or tine-like protrusion attachmentstructures (hereafter referred to as “tines” for convenience) will bediscussed. These leads may be implanted through a septum in the heart asdiscussed above. Collectively, FIGS. 10-13 describe a variety ofcomponents that may be incorporated into such a lead.

FIG. 10 depicts a relatively simple embodiment of a lead 1000 thatincorporates tines. The distal end of the lead 1000 is on the left sideof FIG. 10. The lead 1000 includes two sets of tines 1004 and 1006 thatare oriented in opposite directions.

When the lead is implanted, the first set of tines 1004 attached to thedistal portion of the lead 1000 is maneuvered through the access tunnelin the septum (not shown). The tines 1004 may be oriented andconstructed so that they will collapse when passing through the accesstunnel.

After the tines 1004 pass through the access tunnel the tines 1004 maybe expanded and then positioned against a septal wall in the left sideof the heart (e.g., the left atrium, not shown). In this configuration,the tines 1004 may prevent the lead 1000 from being pulled back out ofthe access tunnel. For example, after the tines 1004 have passed intothe left side of the heart, pulling the lead 1000 back toward the rightside of the heart may cause the tines 1004 to open when they contact theseptal wall. As a result, the tines 1004 will tend to prevent the distalend of the lead 1000 from being pulled back into the right side of theheart.

A second set of tines 1006 extending from the lead 1000 may bepositioned against the opposite side of the septal wall (e.g., in theright atrium, not shown). The tines 1006 may help prevent the lead 1000from extending further into the left side of the heart.

As described in more detail below, the tines 1006 and 1004 may beoriented in opposite directions so that the tines will tend to lock thelead 1000 in place on the septum. For example, the tines 1006 may beoriented so that they will tend to open when they contact the septalwall as the lead 1000 is pushed toward the left side of the heart.

In some embodiments the tines 1004 and 1006 are positioned a givendistance D apart on the lead 1000. For example, the lead 1000 may beconstructed so that the spacing D between the tines 1004 and 1006 isapproximately equal to the thickness of the septum in the area of theaccess tunnel. In some patients this thickness is approximately 3-4 mmin the area of the fossa ovalis.

The lead 1000 also includes a sensor 1008 for measuring pressure in theleft side of the heart, a sensor 1010 for measuring pressure in theright side of the heart, a ring electrode 1012 that may be used forunipolar pacing of the septum and an electrode 1014 that may be used inconjunction with the electrode 1012 for bipolar pacing or sensing.Electrical wires (not shown) in the lead 1000 connect the sensors 1008and 1010 and the electrodes 1012 and 1014 to the device 100 (not shown).

In some embodiments the tines are slidably mounted to the lead so thatthe tines may be moved toward one another to firmly attach the lead tothe septum. Such movement of the tines may be accomplished, for example,by a manual operation (e.g., via a tensile member or sheath) orautomatically through the use of a biasing member (e.g., a spring).

FIG. 11 depicts an embodiment of a lead 1100 that incorporates two setsof tines 1104 and 1106 where the set of tines 1106 is slidably mountedto the lead 1100. In this embodiment the position of the tines 1106relative to the tines 1104 may be adjusted in a longitudinal directionrelative to the lead 1100. In this way the tines 1104 and 1106 may bepressed against opposite septal walls to effectively lock the tines tothe septum (not shown).

In some embodiments the slidable attachment consists of one or moretongue structures 1108 on the tines 1106 and one or more correspondinggroove structures 1110 on the lead 1100. Thus the tines 1106 may be slidalong the groove between the position shown and the position representedby the dashed lines 1112.

In some embodiments, once the slidable tines 1106 are positioned on thelead 1100 they may be held in place (e.g., prevented from sliding) onthe lead 1100 by friction between a support structure 1114 for the tines1106 and a surface 1116 of the lead 1100. Alternatively, an activeholding structure (not shown) may be used to fix the position of thetines 1106 relative to the lead 1100.

The lead 1100 may include a tensile member such as a stylet 1118 thatslides within the lead 1100 and is attached to the tines 1106 or thesupport structure 1114. In this case, sliding the tensile member 1118will cause the tines 1106 to slide toward or away from the tines 1104.As shown in FIG. 11, the stylet may be enclosed in a lumen 1120 in thelead. In addition, a handle (not shown) may be connected to the tensilemember 1118 at the proximal end of the lead 1100.

It should be appreciated, however, that other techniques for moving thetines may be used. For example, the lead 1100 may include a sheath (notshown) that slides in a longitudinal direction relative to the lead 1100as described above in conjunction with FIG. 6. The sheath, in turn, maybe attached to the slidable tines 1106. Thus, the tines 1106 may be slidtoward the tines 1104 by sliding the sheath. In this way, when the tines1104 and 1106 are positioned on opposite sides of the septum the tines1104 and 1106 may be firmly pushed up against respective septal walls.In addition, the applied force may serve to further spread the tines1104 and 1106 so that the tines 1104 and 1106 will lie flatter againstthe septal walls. As is known in the art, the proximal side of thesheath may be attached to a handle or some other structure thatfacilitates sliding the sheath.

In some embodiments the sheath may be releasably attached to the tines1106 so that the sheath may be withdrawn from the tines 1106 asdescribed above in conjunction with FIG. 6. For example, the sheath maybe constructed so that it is not actually attached to the tines 1106,but merely abuts against the proximal side of the tines 1106 to push thetines 1106 toward the distal end of the lead 1100.

The lead 1100 includes one or more sensors to sense pressure on the leftside of the heart (sensor 1122) and on the right side of the heart (notshown). Electrical wires (not shown) in the lead 1100 connect thesensors (e.g., sensor 1122) to the device 100 (not shown).

The embodiment of FIG. 11 illustrates that the tines 1104 and 1106 mayincorporate electrodes 1124. The electrodes 1124 may be used, forexample, to pace the septal walls or sense in the vicinity of theseptum. Alternatively, the tines 1104 and 1106 may be constructed of anelectrically conductive material (e.g., a biocompatible metal or aconductive polymer) so that the tines 1104 and 1106 also function aselectrodes. The conductive polymer may consist of, for example, siliconerubber with conductive micro or nano particles. The particles maycomprise, for example, gold, platinum, iridium, carbon nanotubes ortitanium. Electrical wires (not shown) in the lead 1100 connect theelectrodes 1112 or tines to the device 100 (not shown).

The embodiment of FIG. 11 also illustrates that the lead 1100 mayinclude a relatively sharp distal end 1126. As discussed above, thesharp end 1126 may be used to pierce through the septum to create anaccess tunnel that enables the distal portion of the lead 1100 to passinto the left side of the heart.

FIG. 12 depicts an embodiment of a lead 1200 that incorporates two setsof tines 1204 and 1206 that are biased toward one another by a biasingmember. In this embodiment, the second set of tines 1206 is attached tothe biasing member and slidably mounted to the lead 1200 (e.g., asdiscussed above). The biasing member is configured to force the tines1206 toward the tines 1204. In this way the tines 1204 and 1206 may bebiased against opposite septal walls (not shown) to actively lock thetines 1204 and 1206 to the septum. As a result, the spacing between thetines 1204 and 1206 may be automatically adjusted according to the widthof the septum. In addition, the force applied by the biasing member mayserve to further spread the tines 1204 and 1206 radially from the lead1200 so that the tines 1204 and 1206 will lie flatter against the septalwalls.

In FIG. 12 the biasing member incorporates a spring 1208 that isconnected to the slidable tines 1206. The spring 1208 is also connectedto the lead 1200 using, for example, a fastener mechanism 1214. As aresult, the spring 1208 may bias the tines 1206 towards the tines 1204.Thus, when the tines are expanded (e.g., as depicted for tines 1204)from the lead 1200 on opposite sides of a septum, the spring 1208 may beused to pull the two sets of tines together so that they are firmly heldto their respective septal walls.

As another example, in an embodiment that does not use the sheath 1212discussed below, when the tines 1204 are pushed through the accesstunnel the orientation of the tines 1206 may prevent the tines 1206 frompassing into the access tunnel. As a result, the spring 1208 will expandas the proximal end of the lead 1200 is pushed further into the accesstunnel. After the tines 1204 pass through the access tunnel, they willexpand out from the lead 1200. When this happens the physician willrelease the distal pressure on the lead 1200 and the spring 1208 willpull the two sets of tines 1204 and 1206 toward one another. As aresult, the tines will be effectively locked against the septum.

It should be appreciated that other orientations may be used for thebiasing member. For example, a spring may be positioned on the rightside of the tines 1206. In this case, the spring may attach to the lead1200 to the right of the tines 1206 in FIG. 12. In addition, the springmay initially be configured to not engage the slidable tines 1206. Inthis case a trigger mechanism may be used to release the spring toengage the slidable tines 1206.

FIG. 12 also illustrates that the tines 1204 and 1206 may includebiasing members 1210 each of which cause one or more of the tines toexpand away from the lead 1200. For example the biasing member 1210 mayinclude a relatively simple spring.

Alternatively, the tines 1204 and 1206 may be constructed so that theynaturally tend to expand away from the lead 1200. For example, the tinesmay be made of a piece of elastic metal that is bent to be in anextended position. In this case the elasticity of the metal may permitthe tines to be bent to a non-extended position (e.g., a position wherethe tines lie against the lead) when a force is applied, yet the tineswill go back to their original position when the force is removed.

The lead 1200 also may include a sheath 1212 that slides relative to thelead 1200. The sheath 1212 may be used to hold the tines 1204 and 1206in a non-extended position (e.g., the position depicted for tines 1206)when the lead 1200 is being installed. After the lead 1200 has beenproperly positioned in the heart, the sheath 1212 may be pulled towardthe proximal end of the lead 1200 to release the tines. As mentionedabove, the proximal side of the sheath may be attached to a handle orsome other structure that facilitates sliding the sheath 1212.

The lead 1200 also include two pressure sensors S1 and S2. As discussedabove, these sensors may be used to measure pressure in the left andright sides of the heart.

FIG. 13 is an end view of two set of tines on a lead 1300 thatillustrates that each set of tines may have a different orientation withrespect to a cross section of the lead 1300. The orientation of thefirst set of tines 1304 (e.g., tines 1104 in FIG. 11) is shown usingsolid lines. The orientation of the second set of tines 1306 (e.g.,tines 1106 in FIG. 11) is shown using dashed lines. One advantage ofusing different orientations for the two sets of tines is that thesecond set of tines may be less likely to follow the first set of tinesthrough the access tunnel. In addition, the different orientations ofthe tines may provide a more effective lock across the septum.

A variety of different tines or tine-like structures may be used inaccordance with the teachings herein. For example, any number of tinesor tine-like protrusions may be used in each set of tines discussedherein.

The tines may be configured to be extendable and retractable. Thisconfiguration may provide, for example, improved maneuverability;particularly when tunneling across the septum.

The tines may be constructed of a variety of materials including, forexample, biocompatible materials such as silicone and polyurethane.Typically the tines would be non-metallic. In some embodiments the tinesmay be constructed of a biodegradable material that degrades over time.This type of material may be used, for example, in a case where it maybe necessary to remove of the lead sometime in the future.

It should be appreciated that the above embodiments depict but a fewexamples of the components that may be incorporated into a leadincorporating tines. A variety of other components including forexample, those described elsewhere herein, may be incorporated into sucha lead. For example, in the illustrated embodiments these leads includea sensor on their distal portions that are positioned in the left sideof the heart when the lead is implanted to monitor pressure in the leftside of the heart. It should be appreciated, however, that such leadsmay incorporate other sensor configurations in accordance with theteachings herein.

Referring now to FIGS. 14-19, various embodiments of leads thatincorporate one or more disk, membrane or membrane-like attachmentstructures (hereafter referred to as “membranes” for convenience) willbe discussed. FIG. 14 depicts a lead implanted through a septum (theatrial septum in this example) in the heart. FIGS. 15-19 illustratevarious components that may be incorporated into a lead.

In FIG. 14, a lead 1400 may be initially introduced into the heart viathe right atrium RA as discussed above in conjunction with FIG. 3. Thelead 1400 is then passed through to the left atrium after an accesstunnel is created in the atrial septal wall using, for example, apiercing tool (not shown). The distal portion of the lead 1400 is thenmaneuvered through the access tunnel so that a flexible diaphragm 1402on the distal end of the lead 1400 protrudes into the left atrium LA.

The flexible diaphragm 1402 comprises part of a sensor assembly thatmeasures pressure in the left side of the heart. In some embodiments theflexible diaphragm 1402 comprises part of pressure sensor. In someembodiments the flexible diaphragm 1402 is used to couple pressure wavesfrom the left side of the heart to a sensor in the lead via afluid-filled chamber (e.g., a lumen).

The distal end of the lead 1400 may include a membrane 1404 that isimplanted into the left atrium. In some embodiments the membrane 1404has sufficient elasticity such that it tends to expand radially outwardfrom the lead 1400. In this way the membrane 1404 may be maneuvered tolie relatively flat against a septal wall 1408 to fix the lead 1400 tothe septum.

The lead 1400 may include a membrane 1406 located proximally from theend of the lead 1400. The membrane 1406 also may have sufficientelasticity such that it tends to expand radially outward from the lead1440. Thus, the membrane 1406 may be maneuvered to lie relatively flatagainst a septal wall 1410 to fix the lead 1400 to the septum.

The lead 1400 also may include one or more electrodes (e.g., a ringelectrode) that are used to apply stimulation signals to the septum orsense signals in the area of the septum. For example an electrode 1412may be located a short distance away from the proximal side of themembrane 1404 and an electrode 1414 may be located a short distance awayfrom the proximal side of the membrane 1406. The electrode 1412 may, forexample, be used for unipolar pacing of the septum or sensing in theseptal area. The electrode 1414 may, for example, be used for bipolarsensing of the septum in conjunction with a sensing electrode 1412 orfor unipolar sensing. To reduce the complexity of FIG. 14, theelectrical connections between the electrodes and the device 100 are notshown.

FIG. 15 depicts the distal end of one embodiment of a lead 1500incorporating two membrane attachment structures 1502 and 1504. Themembrane 1502 is attached to the distal end of the lead 1500. Themembrane 1504 is attached to the lead 1500 on the proximal side ofmembrane 1502. Typically, the distance between the two membranes 1502and 1504 is approximately equal to the width of the septum in the areaof the access tunnel through the septum (not shown).

In some embodiments, (e.g., as discussed herein for other attachmentstructures) one or both of the membranes 1502 and 1504 may be slidablymounted to the lead 1500. For example, the lead 1504 may slide on theoutside of the body of the lead 1500. In addition, a biasing member suchas a spring (not shown) may be used as described herein to bias themembranes 1502 and 1504 to automatically adjust to various septal wallthicknesses. These features may enable the membranes 1502 and 1504 to bemore firmly placed against the walls of the septum.

The membranes 1502 and 1504 may be constructed to lie relatively flatagainst a septal wall and to have a relatively low profile. Thus, themembranes 1502 and 1504 may serve to securely attach the lead 1500 tothe septum without encroaching too far into the left side of the heart.Due to this low profile and the formation of the intima the likelihoodof blood clots breaking loose may be significantly reduced as comparedto leads that protrude relatively deeply into the left side of theheart.

The membranes 1502 and 1504 may be constructed using a variety ofmaterials. For example, the membranes 1502 and 1504 may be constructedof silicone, a Dacron mesh or a cloth-like material.

Once the lead 1500 is secured in place (e.g., by appropriate placementand by the formation of the intima), a flexible diaphragm 1506 locatedat the distal end of the lead 1500 may be used to detect pressure in theleft side of the heart. For example, pressure waves from the left sideof the heart may be transmitted from the flexible diaphragm 1506 to asensor 1508 via a fluid-filled chamber 1510 in the lead 1500.

In some embodiments the flexible diaphragm 1506 may be integral with themembrane 1502. For example, the membrane 1502 may be constructed of aflexible material such as silicone such that the distal side wall of themembrane 1502 serves as the flexible diaphragm 1506. Alternatively, themembrane may include a diaphragmatic portion (similar to a drum) thatenables the transfer of pressure waves from the left side of the heartto the sensor 1508.

In some embodiments the flexible diaphragm 1506 may be a separatecomponent that is attached to the membrane 1502 and/or the body of thelead 1500. In some embodiments the flexible diaphragm 1506 may beconstructed of silicone or a thin metal.

In the embodiment of FIG. 15, an initial fluid-filled chamber defined bya wall 1512 connects via a port 1514 to a lumen 1516 to place the sensorin fluid communication with the flexible diaphragm 1506. In this way,space may be provided in the lead 1500 on the proximal side of the wall1512 for other components (e.g., electrical conductors). In practice,the chamber may transfer the pressure waves from the flexile diaphragm1506 to a sensor located at any location along the length of the lead1500 (e.g., sensor 1508) or located in the device 100 (not shown).

The sensor 1508 includes a flexible diaphragm 1518 that moves inresponse to pressure waves in the fluid-filled lumen 1516. In accordancewith the received pressure waves, the pressure sensor 1508 generateselectrical signals that are transmitted to the device 100 (not shown)via one or more electrical leads 1520. As discussed above, the device100 may then be configured to provide this pressure information to anexternal device or to provide appropriate therapy to the patient inresponse to the pressure signals.

The lead 1500 also may include one or more electrodes as discussedherein. For example a ring electrode 1522 may be located between themembranes 1502 and 1504 for unipolar pacing of the septum. One or moreelectrical conductors 1524 connect the electrode 1522 with the device100. In some embodiments a membrane may be constructed of a conductingpolymer. In this case, an electrical conductor (not shown) connected tothe membrane may provide electrical signals from the device 100 (notshown) for pacing the septum.

FIG. 16 depicts an alternative embodiment where a lead 1600 includes apressure sensor 1602 mounted on its distal end. The sensor 1602 includesa flexible diaphragm 1604 on one end and a chip 1606 (e.g., apiezoelectric element). Pressure waves from the flexible diaphragm 1604are transferred to the chip 1606 via a fluid-filled chamber 1608 in thesensor 1602. In accordance with the received pressure waves, thepressure sensor 1602 generates electrical signals that are transmittedto the device 100 (not shown) via one or more electrical leads 1610.

In some embodiments, an attachment structure 1612 is attached to thelead 1600 around the sensor 1602. For example, a flexible membrane,tines or other structures may be mounted on the periphery of the sensor1602.

FIG. 17 depicts one embodiment of a sensor mounted on the distal end ofa lead 1700. In this example, a sensor 1702 is attached to an end 1704of a lead body 1706. Typically, the sensor 1702 and the lead body 1706would have the same diameter. Thus, they may be configured in aco-circumferential orientation. The sensor 1702 may be attached to thelead body 1704 by a variety of techniques including, for example, laserwelding and adhesive attachment (e.g., using an epoxy).

The sensor includes a flexible diaphragm 1708 at its distal end. Thesensor case and flexible diaphragm are shown in an exploded view toillustrate one technique for attaching the flexible diaphragm 1708 tothe sensor case. Specifically, the flexible diaphragm 1708 may be formedwith a lip that is placed over a seat provided on the end of the sensorcase. Thus, an inside surface 1710 of the lip may, for example, beadhered to an outside surface 1712 of the seat. The lip of the flexiblediaphragm 1708 may be attached to the seat of the sensor body using avariety of techniques including, for example, laser welding and adhesiveattachment (e.g., using an epoxy). The configuration of FIG. 17 mayprovide an advantageous form of attachment in that welding may beavoided on the end portion of the flexible diaphragm. Thus, stressesand/or damage may be avoided on the portion of the diaphragm that flexesin response to pressure waves.

In general, various aspects of the sensor may be constructed using knownmaterials and techniques. For example, the sensor case may beconstructed of a variety of materials including, for example, titaniumor another biocompatible metal. The sensor may include apressure-to-electrical transducer 1716 such as a piezoelectric chip. Oneor more electrical conductors 1718 are routed out the proximal end ofthe sensor 1702 through the lead 1700 to connect the sensor 1702 to thedevice 100 (not shown).

The case interior 1714 may be filled with a biocompatible fluid or gelsuch as, for example, silicone oil. A port 1720 may be provided in thesensor case to facilitate filling the interior 1714 with fluid and forremoving bubbles from the fluid. A plug mechanism such as a screw may beused to close the port 1720.

FIG. 18 depicts an embodiment of a lead 1800 where a sensor 1802 isinserted into a distal end of a lead body 1804. The sensor 1802 includesa flexible diaphragm 1806 on its distal end. The lead body 1804 andsensor 1802 are shown in an exploded view to illustrate how thesecomponents may be assembled.

In the embodiment of FIG. 18, the flexible membrane 1806 is attached tothe end of the sensor case. For example, a surface 1808 on the outer rimof the proximal side of the flexible diaphragm 1806 may be affixed to anouter rim surface 1810 of the sensor case. The surfaces 1808 and 1810may be affixed using a variety of techniques including, for example,laser welding and adhesive attachment (e.g., using an epoxy).

The sensor 1802 is inserted into the lead body 1804 as indicated by thearrow 1812. In this case, an outside surface 1814 of the sensor 1802 maybe affixed to an inside surface 1816 of the lead body 1804. Typically,sensor 1802 will be fully inserted into the lead body 1804. Thus, thedistal ends of the lead body 1804 and the sensor 1802 (e.g., theflexible diaphragm 1806) may be aligned. In this case the attachmentstructures (not shown) may be attached to or built into the lead body1804.

FIG. 19 illustrates the distal end of an embodiment of a lead 1900 thatincludes a sheath 1902 that slides over a lead body 1904. The sheath1902 may be used, for example, to cover flexible membranes 1906 attachedto the lead when the lead is being implanted. This may improve themaneuverability of the lead and/or simplify the implantation procedure.The sheath 1902 may be removed from the lead 1900 once the flexiblemembranes 1906 are properly positioned.

FIG. 19 also illustrates an embodiment where a membrane 1906 is slidablymounted to the lead 1900. As described above, a membrane 1906 may slideon the outside of the body of the lead 1900 where the travel of themembrane is restricted by a tongue 1908 and groove 1910 structure. Inaddition, a biasing member 1912 such as a spring may bias a membrane1906 to automatically adjust to various septal wall thicknesses.

Referring now to FIGS. 20-22, various embodiments of leads thatincorporate one or more inflatable membrane or balloon-like attachmentstructures (hereafter referred to as “balloons” for convenience) will bediscussed. The distal end of a lead including such a balloon may beimplanted in the left side of the heart (e.g., the left atrium) asdiscussed above in conjunction with FIG. 14. During implantation, theballoon typically would be deflated. After the balloon is maneuvered toa desired location (e.g., against a septal wall in the left atrium), theballoon is inflated and serves to fix the lead to the septum. The distalend of the lead may include a pressure sensor or it may include aflexible diaphragm that is used to couple pressure waves from the leftside of the heart to a sensor in the lead via a lumen filled with afluid. Thus, the lead may be used to accurately measure pressure in theleft side of the heart.

FIG. 20 depicts the distal end of one embodiment of a lead 2000 thatincorporates two balloons 2002 and 2004. The balloon 2002 is located onthe distal end of the lead 2000 and is implanted on the left side of aseptal wall 2006 (e.g., in the left atrium “LA”). The second balloon2004 is located on the lead 2000 so as to be located on the right sideof the septum 2006 when the lead 2000 is implanted. By properly sizingand positioning the balloons 2002 and 2004, then controlling theexpansion of the balloons 2002 and 2004, the expanded balloons 2002 and2004 may be firmly pressed against each side of the septum 2006 tosecurely fix the lead 2000 to the septum.

In the embodiment of FIG. 20 each balloon is in fluid communication witha fluid-filled chamber 2008 (e.g., a lumen) in the lead 2000. Forexample, the balloons 2002 and 2004 may include ports 2010 and 2012,respectively that provide paths for fluid flow between the balloons 2002and 2004 and the chamber 2008.

The chamber 2008 may be accessible at or near the proximal end of thelead 2000. An inflation device (not shown) may be attached to theproximal end of the chamber 2008 to inflate the balloons 2002 and 2004after they are positioned across the septum 2006.

Once inflated, the balloons 2002 and 2004 serve to fix the lead inplace. For example, the balloon 2002 may be positioned against a septalwall 2014 and may prevent the lead 2000 from being pulled in a proximaldirection through the septum 2006. In addition, the balloon 2004 may bepositioned against a septal wall 2016 and may prevent the lead 2000 frombeing extended further into the left side of the heart. Moreover, as thebody may quickly build up the intima over the balloons 2002 and 2004,the balloons 2002 and 2004 may become firmly fixed to the septal walls2014 and 2016, respectively, in a relatively short period of time.

The balloons 2002 and 2004 may be constructed to lie relatively flatagainst the septal walls 2014 and 2016 and to have a relatively lowprofile. Thus, the balloons 2002 and 2004 may serve to securely attachthe lead 2000 to the septum 2006 without encroaching too far into theleft side of the heart. Due to this low profile the likelihood of bloodclots breaking loose may be significantly reduced as compared to leadsthat protrude relatively deeply into the left side of the heart.

Once the lead 2000 is secured in place, a flexible diaphragm 2018located at the distal end of the lead 2000 may be used to detectpressure in the left side of the heart. For example, pressure waves fromthe left side of the heart will be transmitted by the flexible diaphragm2018 to the adjacent fluid-filled chamber 2008. The fluid in the chamber2008 transmits the pressure waves from the flexile membrane 2018 to asensor located at a location along the length of the lead 2000 (e.g.,sensor 2020) or located in the device 100 (sensor not shown).

In some embodiments the flexible diaphragm 2018 may be part of theballoon 2002. In other embodiments, however, the flexible diaphragm 2018may be a separate component of the lead 2000. Examples of variousconfigurations are discussed below.

In accordance with the received pressure waves, the pressure sensor 2020generates electrical signals that are transmitted to the device 100 (notshown) via one or more electrical conductors 2022. The electricalconductors 2022 may be routed through the lead 2000 via a lumen 2024. Asdiscussed above, the device 100 may then be configured to provide thispressure information to an external device or to provide appropriatetherapy to the patient in response to the pressure signals.

The lead 2000 also may include one or more electrodes that may be usedto apply stimulation signals to the septum or sense signals in the areaof the septum. For example, a first ring electrode 2026 may be locatedbetween the balloons 2002 and 2004 for unipolar pacing of the septum2006. In addition, a second ring electrode 2028 may be incorporated intothe lead 2000 proximal to the second balloon 2004 to provide bipolarpacing or sensing in conjunction with the electrode 2026. The electricalconnections between the electrodes 2026 and 2028 and the device 100 maybe routed through the lumen 2024 as represented by the dashed line 2030.

In the embodiment of FIG. 20 the balloons 2002 and 2004 may be inflatedby forcing fluid into the chamber 2008. Under pressure, the fluid isforced through ports 2010 and 2012 into the uninflated balloons 2002 and2004. Thus, in this embodiment, the balloons are filled with the samefluid that is used to transmit pressure waves from the flexiblediaphragm 2018 to the sensor 2020.

FIG. 21 illustrates an alternative embodiment of a lead 2100 that usesseparate fluid paths for pressure wave transmission and ballooninflation. Fluid in a sealed chamber 2102 is used to transmit pressurewaves from a flexible diaphragm 2104 at the distal end of the lead 2100to a flexible diaphragm 2106 of a sensor 2108. A wall 2110 may be usedto seal the chamber 2102 from other areas within the lead 2100.

The lead 2100 may include a port 2112 for filling the chamber 2102. Asdiscussed above, once the chamber 2102 has been filled and all bubblesremoved from the fluid, the port 2112 may be sealed using, for example,a screw (not shown).

A separate lumen 2114 is used to fill a balloon 2116. Fluid from thelumen 2114 is forced through a port 2118 into the interior of theballoon 2116. In this case the shape of the balloon 2116 may take theform of a doughnut since the balloon 2116 surrounds the circumference ofthe chamber 2102.

One or more electrical conductors 2120 from the sensor may be routed tothe device 100 (not shown) via another lumen 2122. In this case, anentrance port 2124 to the lumen may be sealed to prevent fluid flow toor from the lumen 2122 and the chamber 2102.

In the embodiment of FIG. 20 the balloons 2002 and 2004 are in fluidconnection with a common fluid carrying chamber. As a result, bothballoons 2002 and 2004 are inflated at the same time after they arepositioned at the desired location.

In some embodiments separate lumens may be used to inflate two or moreballoons. For example, FIG. 22 depicts a distal portion of oneembodiment of a lead 2200 where a first lumen 2202 is in fluidcommunication with a first balloon 2204 and a second lumen 2206 is influid communication with a second balloon 2208. Inflation/deflation ofeach of the balloons 2204 and 2208 may then be individually controlledby one or more fluid injection systems 2210 connected to the proximalends of the lumens 2202 and 2206. That is, the fluid injection system(s)2210 may cause fluid to flow between the lumens 2202 and 2206 and theballoons 2204 and 2208 via ports 2212 and 2214, respectively.

FIG. 22 illustrates an embodiment where a sensor 2216 may be located atthe end of the lead 2200. The sensor 2216 may take a form described, forexample, in conjunction with FIGS. 16-18. Thus, pressure waves in theleft side of the heart cause movement of a flexible diaphragm 2218 inthe sensor 2216 which causes the sensor to transmit correspondingelectrical signals via one or more electrical conductors 2220.

In some embodiments, the second balloon 2208 may incorporate one or moreflexible diaphragms 2222 to detect pressure in the right side of theheart. To this end the flexible diaphragm 2222 and a flexible diaphragm2226 of a second sensor 2224 may be in fluid communication with a commonfluid. For example, as shown in FIG. 22, the fluid used to inflate theballoon 2208 may be used to carry pressure waves from the flexiblediaphragm 2222 to the sensor 2224.

FIG. 22 also illustrates that a separate lumen 2228 may be used to routethe electrical conductors from the components on the distal end of thelead 2200 to the device 100 that provides signal processing. Forexample, in some embodiments the signal processing may generatestimulation signals that are transmitted over an electrical conductor2230 to a ring electrode 2232. In some embodiments the signal processingmay receive bipolar signals via a conductor 2234 from an electrode 2236and the conductor 2230 from the electrode 2232 to sense electricalactivity in the vicinity of the distal end of the lead 2200.

In some embodiments the deflated balloons may be formed to lierelatively flat against the intra cardiac lead. As a result, the leadmay be easily maneuvered though the body and the access tunnel. In someembodiments a moveable sheath may be used to encase the balloons asdescribed above in conjunction with FIG. 19. The sheath may be used toensure that the balloons do not interfere with the maneuvering of alead. In this case, the sheath may be removed from the lead once theballoons are properly positioned.

It should be appreciated that a variety of lead structures andconfigurations may be used in accordance with the teachings herein. Forexample, a lead body may be constructed using a variety of materials asdiscussed above. In addition, the balloons may be formed in variousshapes and constructed of various materials. For example, the balloonsmay be constructed using biocompatible material such as silicone rubberor polyurethane.

A variety of fluids may be used to inflate the balloons and/or transmitpressure waves. For example, the fluid may consist of a biocompatibleliquid such as water, saline or silicone oil. In some applications,however, the liquid needs to be compatible with gas sterilizationprocedures that may be used to sterilize the lead.

FIGS. 23 and 24 illustrate an alternative embodiment of a sensor thatincorporates a bellow for sensing pressure changes in the left side ofthe heart. Such a configuration typically would be used in embodimentswhere the sensor is located at the distal end of a lead.

FIG. 23 depicts an exploded view of one embodiment of a sensor 2300incorporating a flexible bellow 2302. A main sensor body 2304incorporates a pressure-to-electrical transducer 2306 that generateselectrical signals provided to an electrical conductor 2308.

The main sensor body 2304 also includes a seat 2310 adapted to receive abase portion 2312 of the bellow 2302. An inside surface 2314 of the baseportion 2312 may, for example, be adhered to an outside surface of theseat 2310 using a variety of techniques including, for example, laserwelding and adhesive attachment (e.g., using an epoxy).

The distal end of the bellow comprises a wall or end piece 2316 thatforms the distal end of the sensor assembly 2300. The interior 2318 ofthe bellow and the main body 2304 may then be filled with anon-compressible fluid.

In some embodiments, the sensor may include a bellow cover 2320. Thebellow cover 2320 may facilitate attaching the sensor 2300 to a lead.For example, an attachment structure such as tines may be affixed to theoutside of the bellow cover 2320. In addition, the bellow cover 2320 mayinclude a lip 2322 to which an attachment structure such as a flexiblemembrane or balloon may be attached.

A base portion of the bellow cover 2320 may be adapted to be affixed tothe base portion 2312 of the bellow 2302. An inside surface 2324 of thebase portion of the bellow cover 2320 may, for example, be adhered to anoutside surface of the base 2312 using a variety of techniquesincluding, for example, laser welding and adhesive attachment (e.g.,using an epoxy).

FIG. 24 illustrates the distal end of one embodiment of a lead 2400 thatincorporates a bellow-based sensor 2402. The sensor 2402 and anattachment structure 2404 such as a membrane or a balloon are mounted onthe distal end of the lead 2400.

A portion of a distal surface 2406 of the attachment structure 2404 maybe affixed to a lip 2408 of a bellow cover 2410 on the sensor 2402. Thisfixation may be accomplished using a variety of techniques including,for example, laser welding and adhesive attachment (e.g., using anepoxy).

In operation, changes in pressure in the left side of the heart willcause a distal surface 2412 of a bellow 2414 in the sensor 2402 to move.In general, the bellow 2414 may expand and contract in the direction ofthe arrows 2416.

Here, provisions may be taken to prevent blood from the left side of theheart from flowing into a space 2418 between the bellow 2414 and thebellow cover 2410. For example, a thin flexible diaphragm (e.g., made ofsilicone) may attached over the surface 2406 including the surface 2412of the bellow to prevent ingression of blood into the space 2418.

Referring now to FIGS. 25-28 various embodiments of leads thatincorporate circumferential tine attachment structures will bediscussed. In some embodiments the circumferential tines take the formof spiral or spiral-like protrusions (hereafter referred to as “spirals”for convenience). Typically, this type of lead includes a sensor on itsdistal end such that the sensor may be positioned in the left side ofthe heart when the lead is implanted. In this way, the lead may be usedto monitor pressure in the left side of the heart (e.g., the leftatrium).

FIG. 25 illustrates the distal portion of one embodiment of a lead 2500incorporating two oppositely oriented involuted spiral attachmentstructures 2504 and 2506. Before implantation, the involuted spiralportions 2504 and 2506 of the lead 2500 are maintained in a relativelystraight configuration within the distal portion of a lead body 2502.

In some embodiments the involuted spirals contained within the lead 2500and are held relatively straight by a tensile member such as a stylet(not shown) in the lead 2500. The lead 2500 may thus be maneuvered toand through the septum 2514 using a stylet as discussed above. After thedistal portion of the lead 2500 is inserted into the left side of theheart, the stylet may be retracted to allow the spiral 2504 to unwindonto the septal wall 2510. The second spiral 2506 may then be unwoundonto the septal wall 2512 by further retraction of the stylet.

Each spiral 2504 and 2506 is formed so that it lies relatively flatagainst its respective septal wall 2510 and 2512. In this way, the leadmay be firmly attached to the septum 2514 yet have a relatively lowprofile in the left side of the heart.

In some embodiments, a pressure sensor 2508 may be incorporated in thespiral 2504. In this case, the pressure sensor 2508 may be positionedagainst the septal wall 2510 thereby providing a relatively low profilesensor in the left side of the heart. Accordingly, the lead 2500 may beused to provide relatively safe and accurate pressure measurements fromthe left side of the heart (e.g., the left atrium).

As FIG. 25 illustrates the two involuted spirals 2504 and 2506 may beconfigured so that one turns in a clockwise direction and the otherturns in a counterclockwise direction. This configuration providesrelatively stabile mechanism for securely locking the lead 2500 to theseptum 2514.

In some applications, the use of involuted spirals instead of standardspirals may provide a closer fit against the septal walls 2510 and 2512.It should be appreciated, however, that a variety of spiral and othercurved protrusions may be used in accordance with the teachings herein.

FIG. 26 is an example of a side view of a lead 2600 that shows how aspiral 2604 and a sensor 2612 may lie relatively flat against a septalwall 2608. Similarly, a spiral 2606 lies relatively flat against aseptal wall 2610.

FIG. 26 also illustrates that the lead 2600 may include one or moreelectrodes 2614 and other sensors 2616. The construction and operationof these components may be similar to the construction and operation ofother electrodes and sensors discussed herein.

FIG. 27 illustrates that in some embodiments the radius R of a spiral2600 that includes a pressure sensor must be equal to or greater thanthe length of the pressure sensor. In this configuration all of theturns of the spiral may easily unwind one around the other.

FIGS. 28A and 28B illustrate how the retraction of a stylet 2804 in alead 2800 may cause the distal end of the lead 2806 to return to thespiral shape. In some embodiments separate removable stylets may be usedto straighten each involuted spiral for the initial implantationprocedure. Alternatively the lead may be configured so that a singlestylet is used to straighten both spirals.

The use of the stylet 2804 may also enable removal of the lead 2800after it has been implanted. For example, by reinserting the stylet 2804into the lead 2800 the spirals may be straightened out therebyfacilitating removal of the lead from the septum.

FIGS. 29-31 illustrate the distal ends of several embodiments of leadsthat incorporate attachment structures that take the form of a J-lead. AJ-lead structure on the distal ends of the leads may be used to providea relatively secure and low profile attachment to a septal wall on theleft side of the heart. In addition, the J-lead portion may accommodatea sensor, thereby enabling accurate pressure measurements in the leftside of the heart.

FIG. 29 illustrates the distal end of one embodiment of a lead 2900incorporating a J-lead structure 2902. During implantation, the J-leadstructure 2902 is maneuvered through a septum 2904 so that the end ofthe J-lead rests against a septal wall 2906 in the left side of theheart.

In some embodiments the J-lead structure incorporates a pressure sensor2908. As FIG. 29 illustrates, with an appropriate configuration of theJ-lead 2902, the sensor 2908 and the J-lead may exhibit a relatively lowprofile in the left side of the heart. In the embodiment of FIG. 29, thesensor 2908 may be installed in the lead 2900 such that a flexiblediaphragm 2914 in the sensor forms a portion of the exterior surface ofthe lead 2900.

FIG. 29 also illustrates that the lead 2900 may include one or moreelectrodes 2910 for pacing and/or sensing in the septal area. Inaddition, the lead 2900 may include other pressure sensors as discussedherein. For example, a pressure sensor 2912 may be used to obtainpressure measurement in the right side of the heart.

FIG. 30 illustrates the distal end of a lead 30 where a J-lead structure3002 include a flexible diaphragm 3004 that may be positioned in theleft side of the heart. The lead 3000 also includes a fluid-filledchamber (e.g., a lumen) 3006 that is used to transmit pressure wavesfrom the flexible diaphragm 3004 to a pressure sensor located anywherewithin the lead 3000 (e.g., sensor 3008) or a pressure sensor located inthe device 100 (not shown).

FIG. 30 also illustrates that the lead 3000 may incorporate one or moreattachment structures 3010. For example, a tine, membrane, balloon orspiral structure as discussed herein may be used to help prevent thelead 3000 from encroaching further into the left side of the heart. Inaddition, as discussed herein the attachment structures 3010 may beadjustable (e.g., slidably mounted on the lead 3000).

In some embodiments the radius of the J-lead structure 3002 may besufficiently small so that the J-lead structure 3002 may be insertedthrough an access tunnel in a septum. In some embodiments the J-leadstructure 3002 comprises a relatively tight loop. For example, such aloop may form almost a full circle.

In some embodiments a tensile member such as a stylet (not shown) may beincorporated into the lead to substantially straighten the J-leadstructure during the implantation procedure. One example of thisconfiguration is illustrated in FIG. 31.

In FIG. 31 a lead 3100 includes a lumen 3102 which, in turn, carries astylet 3104. When the stylet 3104 is fully inserted into the lumen 3102the shape of the lead 3100 may be controlled by the stylet 3104. As aresult, the distal end of the lead 3100 may be maneuvered to and througha septum (not shown) using the stylet 3104 as discussed above. After thedistal portion of the lead 3100 is inserted into the left side of theheart, the stylet may be retracted to allow the J-lead structure tocurve onto the septal wall.

In some embodiments the shape of the J-lead structure may be defined byone or more springs 3106 in the lead 3100. It should be appreciated,however, that a variety of techniques may be used to provide the desiredshape for the J-lead portion of a lead.

A variety of lead structures and configurations may be used inaccordance with the teachings herein. For example, a lead body may beconstructed using various materials as discussed above. In addition, thespirals and J-leads may be formed in various shapes and constructed ofvarious materials. For example, the spirals and J-leads may beconstructed of biocompatible material such as Nitinol, MP35N, siliconerubber or similar polymers that may be processed into a spiral shape. Anadvantage of Nitinol is that it has relatively good flexibility andmechanical properties.

It should be appreciated from the above description that a variety ofpressure measurements may be made using a lead constructed in accordancewith the teachings herein. For example, referring to FIG. 32, pressurein the thoracic cavity relative to a chamber in the heart may beaccomplished indirectly using one or more leads as described herein. Asrepresented by block 3202, pressure between the thoracic cavity and afirst chamber is initially measured. Then, as represented by block 3204,pressure between the first chamber and a second chamber is measured.Next, as represented by block 3206 the pressure between the thoraciccavity and the second chamber may be calculated by, for example, takingthe difference between the two measurements from blocks 3202 and 3204.Based on this relative thoracic pressure calculation, an appropriateaction (e.g., notification or application of therapy) may be performedas discussed herein (block 3208).

Four examples of relative pressure that may be calculated in accordancewith FIG. 32 follow. Thoracic cavity to left atrium pressure may becalculated by measuring thoracic cavity to right atrium pressure,measuring right atrium to left atrium transmural pressure, then takingthe difference between these two measured pressures. Thoracic cavity toleft ventricle pressure may be calculated by measuring thoracic cavityto right ventricle pressure, measuring right ventricle to left ventricletransmural pressure, then taking the difference between these twomeasured pressures. Thoracic cavity to right ventricle pressure may becalculated by measuring thoracic cavity to left ventricle pressure,measuring left ventricle to right ventricle transmural pressure, thentaking the difference between these two measured pressures. Thoraciccavity to right atrium pressure may be calculated by measuring thoraciccavity to left atrium pressure, measuring left atrium to right atriumtransmural pressure, then taking the difference between these twomeasured pressures.

In embodiments that measure aorta pressure, pressure measurementinformation may be obtained for a variety of clinical applications. Forexample, measurement of aortic pressure may provide some measure ofhypertensive status. In addition, a pressure gradient across the mitralvalve (left atrium to left ventricle pressure measurement) may beobtained as well as a pressure gradient across the aortic valve (leftventricle to aorta pressure measurement).

In addition, as discussed above pressure measurements may be maderelative to the pocket (e.g., can 200) in embodiments where the pressuresensor may be located in the pocket. Thus, the sensor may be vented tothe pocket.

Moreover, a variety of pressure measurements may be made using only asingle lead or a pair of leads. For example, a single lead incorporatinga pair of trans-septal leads (one each for the atrial septum and theventricular septum) and one or more branch leads may be used to measureLV, RV, RA, LA and thoracic pressure. Alternatively two or more leadsmay be configured with various pressure sensors and attachmentstructures to accomplish these measurements.

In view of the above, it should be understood that a lead may beconstructed using various combinations and modifications of thestructures and components described herein. For example, the structureand components described in a given drawing may be used in a leaddescribed in another drawing. In addition, lead components such assensors, electrodes, attachment structures and flexible diaphragms maybe located at various locations on the lead.

In addition, the structures described herein may be implemented in avariety of ways. For example, the leads described herein may be form byattaching various components together. Also, the combinations of some ofthe components which are described herein as being “attached,”“connected” “including,” “affixed,” etc., may be implemented as one ormore integral components.

Referring to FIG. 33, in situations in which arterial pressure is to bemeasured, a lead may be placed through the portion of the septal wallthat separates the right atrial chamber from the root of the aorta. Thistechnique allows for ready access to arterial blood pressure usingtransvenous access techniques. Placement in this location may becompletely analogous to placement of a lead in the left atrium throughthe right atrial septum. In some embodiment this technique involvesrouting the lead to the right atrial chamber (block 3302), piercing theseptal wall that separates the right atrial chamber from the root of theaorta (block 3304) and routing the lead through the septal wall (block3306). Blood pressure measured at the time of implant may be used toconfirm placement in the aorta since aortic pressures are significantlyhigher than left atrial pressure (block 3308). After implantation, thedesired pressure measurements may be taken (block 3310). As discussedherein these pressure measurements may be made with respect to one ormore other pressure measurements.

Referring to FIGS. 34A-34D, thoracic pressure may be accessed by avariety of means. For example, in some embodiments the lead may bepositioned at a location immediately distal to a subclavian or cephalicvein implant site within the rib cage (block 3402) as this location maybe regarded as an intrathoracic pressure site. Typically there is littleor no blood flow through the vein at this location since the vein hasbeen tied off during the implant process. Pressure at this location(block 3404) and, optionally, one or more other locations (block 3406)may then be sensed to provide the desired direct or relative pressuremeasurements (block 3408).

In some embodiments a sensor may be placed in the thoracic space bygoing through the endovascular superior vena cava wall into the thoraciccavity (Block 3412). Pressure at this location (block 3414) and,optionally, one or more other locations (block 3416) may then be sensedto provide the desired pressure measurement (block 3418).

In some embodiments a pressure sensor may be placed through the rightatrial wall or right ventricular wall into the pericardial space (block3422). It should be noted here that the pressure in the pericardial sacmay approximate intrathoracic pressure with exception of situations inwhich the heart is not excessively enlarged or in situations in whichpericardial fluid has accumulated. This is typically caused bypathologic events leading to pericardial effusion secondary totamponade, trauma, or inflammatory process leading to fluid ingressioninto the pericardial space. Thus, in some embodiments pressure may bemeasured in the pericardial sac (block 3424). Alternatively, if the leadwith its sensor is advanced even further though the pericardial sac intothe thoracic space (block 3426) thoracic pressure may be directlymeasured (block 3428). Pressure at either of these locations (block 3424or 3428) and, optionally, one or more other locations (block 3430) maythen be sensed to, for example, provide a desired pressure measurement(block 3432).

In some embodiments the sensor lead may be advanced into the coronarysinus, then through the coronary sinus wall into the pericardial space(block 3442). As discussed above pressure may be measured in thepericardial sac (block 3444) or, alternatively, the lead may be routedthrough the pericardial sac into the thoracic cavity (block 3446) toobtain thoracic pressure (block 3448). Pressure at either of theselocations (block 3444 or 3448) and, optionally, one or more otherlocations (block 3450) may then be sensed to provide, for example, adesired pressure measurement (block 3452).

Referring to FIG. 35, in some embodiments left ventricular pressure maybe measured by going through the septum separating the right ventricleand the left ventricle. In this situation a sensor lead may initially beadvanced into the right ventricle and the septal wall pierced (block3502). The lead is then positioned across the septum as discussed above(block 3504). Pressure in the left ventricle (block 3506) and,optionally, one or more other locations (block 3508) may then be sensedto provide a desired pressure measurement (block 3510).

Left ventricular pressure measurement may be most useful for assessingleft ventricular function. This information may be used to aide in drugadministration, for diagnosis of cardiac dysfunction, or for optimizingthe timing such as AV delay, base rate, and V-V timing of an implantablecardiac stimulation device (e.g., a pacemaker). LV pressure and aorticpressure may be used to accelerate or defer shocking the heart duringtachyarrhythmias and thus allow for attempts of ATP or to allow moretime for confirming the presence of a high mortality risk arrhythmia.

It should be appreciated that the applications discussed hereinregarding various embodiments may be applicable to other embodiments aswell. For example, the leads described above may be implanted across anywall including the atrial septum and/or the ventricular septum. Inaddition, the various pressure measurements described above may bemeasured using the various leads described above.

Different embodiments of the stimulation device described above mayinclude a variety of hardware and software processing components. Insome embodiments of the invention, hardware components such ascontrollers, state machines and/or logic are used in a systemconstructed in accordance with the invention. In some embodiments, codesuch as software or firmware executing on one or more processing devicesmay be used to implement one or more of the described operations.

The components and functions described herein may be connected/coupledin many different ways. The manner in which this is done may depend, inpart, on whether and how the components are separated from the othercomponents. In some embodiments some of the connections/couplingsrepresented by the lead lines in the drawings may be in an integratedcircuit, on a circuit board or implemented as discrete wires.

The signals discussed herein may take several forms. For example, insome embodiments a signal may be an electrical signal transmitted over awire while other signals may consist of wireless signals transmittedtrough space. In addition, a group of signals may be collectivelyreferred to as a signal herein.

The signals discussed above also may take the form of data. For example,in some embodiments an application program may send a signal to anotherapplication program. Such a signal may be stored in a data memory.

In summary, the invention described herein generally relates to animproved cardiac pressure sensing apparatus and method. While certainexemplary embodiments have been described above in detail and shown inthe accompanying drawings, it is to be understood that such embodimentsare merely illustrative of and not restrictive of the broad invention.In particular, it should be recognized that the teachings of theinvention apply to a wide variety of systems and processes. It will thusbe recognized that various modifications may be made to the illustratedand other embodiments of the invention described above, withoutdeparting from the broad inventive scope thereof. In view of the aboveit will be understood that the invention is not limited to theparticular embodiments or arrangements disclosed, but is rather intendedto cover any changes, adaptations or modifications which are within thescope and spirit of the invention as defined by the appended claims.

1. A lead configured for measuring pressure in a heart comprising: alead body; a first elastic disk membrane attached to a distal portion ofthe lead body and adapted to attach the lead body to a first side of aseptal wall in a heart, the first elastic disk membrane maneuvered tolie relatively flat against the first side of the septal wall tominimize likelihood of blood clot formation; a second elastic diskmembrane distal to the first elastic disk membrane, the second elasticdisk membrane attached to the distal portion of the lead body andadapted to attach the lead body to a second side of the septal wall inthe heart, the second elastic disk membrane maneuvered to lie relativelyflat against the second side of the septal wall to minimize likelihoodof blood clot formation; and at least one pressure sensor attached tothe distal portion of the lead body and adapted to measure pressure atthe second side of the septal wall in the heart; wherein the secondelastic disk membrane comprises at least one flexible diaphragm, thelead comprising at least one lumen wherein the at least one lumen isfilled with a fluid, wherein the fluid in communication with the atleast one flexible diaphragm, and wherein the fluid is in communicationwith the at least one pressure sensor; and wherein the second elasticdisk membrane and the at least one flexible diaphragm are integral. 2.The lead of claim 1 further comprising additional elastic disk membranesspaced longitudinally along the lead body.
 3. The lead of claim 1comprising at least one flexible diaphragm and at least one lumenwherein the at least one lumen is in fluid communication with the atleast one flexible diaphragm.
 4. The lead of claim 3 wherein the atleast one sensor is in fluid communication with the at least one lumen.5. The lead of claim 1 wherein the at least one membrane has a lowprofile.
 6. The lead of claim 1 comprising a sheath adapted to beslidable over the first elastic disk membrane and the second elasticdisk membrane.
 7. The lead of claim 1 comprising at least one electrodeat the distal portion of the lead body.
 8. The lead of claim 7 whereinthe at least one electrode is configured to pace the heart or sensesignals in the heart.
 9. The lead of claim 1 comprising at least onebranch lead body wherein each branch lead body includes at least onepressure sensor.
 10. The lead of claim 1 wherein the first elastic diskmembrane is slidably mounted to the lead body.
 11. The lead of claim 10comprising at least one biasing member for biasing the first elasticmembrane toward the septal wall in the heart.
 12. The lead of claim 11wherein the at least one biasing member comprises at least one spring.13. The lead of claim 1 wherein the at least one membrane is constructedof silicone or a conducting polymer.
 14. The lead of claim 13 whereinthe conducting polymer functions as an electrode.